In a general mobile communications system, a base station controls uplink data transmission of a UE by sending scheduling signaling. Due to channel fading, the base station may fail to correctly decode uplink data transmitted by the UE.
The 3rd Generation Partner Project (3GPP for short) Long Term Evolution (LTE for short) systems of release 8 to release 11 use hybrid automatic repeat request (HARQ for short) indicator information in a physical HARQ indicator channel of uplink data to indicate whether a base station correctly decodes uplink data transmitted by a UE. However, in the LTE systems of release 8 to release 11, the UE needs to use a common reference signal (CRS for short) as a reference signal to demodulate the indicator information in the physical HARQ indicator channel, determines, according to the indicator information, whether data transmitted in an uplink is correctly decoded, and thereby determines whether to retransmit the data that the base station cannot correctly decode.
With evolution of the LTE systems, in an LTE system of release 12, the CRS is no longer used for demodulation due to its inherent drawbacks. In the LTE system of release 12, a UE-specific demodulation reference signal (DMRS for short) instead of a physical HARQ indicator channel in the LTE systems of release 8 to release 11 is used for demodulation of downlink data transmitted in the system. Therefore, a base station cannot indicate, through the HARQ indicator channel, whether data transmitted by a UE in an uplink is correct and the UE certainly cannot determine whether the data transmitted in the uplink is correctly decoded by the base station. When the base station cannot correctly decode the received uplink data, the base station needs to send new scheduling signaling to instruct the UE to resend the data that the base station cannot correctly decode, which increases signaling load of a control channel of the system.